Why is ATP an important molecule in metabolism?

Question

a. Its terminal phosphate group contains a strong covalent bond that does not contain much chemical energy

b. Its hydrolysis provides an input of free energy for exergonic reactions

c. It provides energy coupling between exergonic and endergonic reactions.

d. It can be used to rediuce NADP+ to create NADPH, an important redox molecule.

e. It permits long-term storage of chemical energy in the cell.

Answer 1

ATP provides energy coupling between exergonic (energy producing) and endergonic (energy requiring) reactions. (c).

When ATP is hydrolyzed to ATP + Pi (broken down), it releases a great deal of energy. (Pi just means inorganic phosphate, PO4-)

ATP+H2​O⇋ADP+Pi​+energy

deltaG of this reaction is about -30 kJ/mol, which means it releases a lot of energy. This is the exergonic reaction.

That energy is used to power energonic reactions, that require energy, and whose delta G values are positive.

You can add together the values from the two coupled reactions to understand how much energy is used or produced overall. One example is the synthesis of glucose and fructose, which gains its energy from the hydrolysis of ATP.

Sucrose + glucose <-> fructose delta G = +27 kJ/mol

ATP + H2O <-> ADP +Pi deltaG = -30 kJ/mol

Sucrose + glucose + ATP <-> fructose + ADP + Pi overall: deltaG = -3kJ/mol

Overall, this coupled reaction releases energy, which makes it favorable in the cell! Process drives normal metabolism.